1. Field of the Invention
The present invention relates to a device and a method for setting belt clamping pressure, and, more particularly, to a belt clamping pressure setting device and method, by which belt clamping pressure is set for a continuously variable transmission (CVT).
2. Description of the Related Art
Conventionally, there has been proposed a CVT hydraulic control device by which clutch pressure for forward and reverse motion can be set in accordance with engine torque in a CVT (for example, refer to the Japanese Patent Application Laid-Open (JP-A) No. 4-357336).
The CVT hydraulic control device judges whether the engine torque has changed or not, and, when it has changed, it judges whether the changed amount is equal to or larger than a predetermined value or not. When the amount is equal to or larger than the predetermined value, a correction amount, by which clutch pressure corresponding to the changed amount is set, for a duty ratio of an electromagnetic valve, is calculated according to a formula (3) disclosed in JP-A No. 4-357336. Then, deterioration in the response of duty control time to torque fluctuations is prevented by directly adding the correction amount to the duty ratio for hydraulic pressure.
The above-described CVT hydraulic control device controls pressure for clamping the CVT belt (belt clamping pressure) so that the pressure is increased at any time when the torque fluctuations are equal to or larger than a predetermined value, regardless of the values of the torque fluctuations, that is, the number of input revolutions of the CVT.
However, there is actually a case in which the belt clamping pressure is sufficient, even if the torque fluctuations are equal to or larger than the predetermined value. Therefore, there has been a problem that there is increased pumping loss in the CVT hydraulic control when the belt clamping pressure is forced to be increased under circumstances in which the torque fluctuations are equal to or larger than the predetermined value, and as a result, the fuel consumption is caused to be lowered.